Interpretive Summary: Foodborne illness outbreaks, particularly involving fresh vegetables and fruits, including melons (cantaloupe, honeydew, and watermelon), and often rare Salmonella serotypes, have increased dramatically over the past 13 years. Despite efforts to mitigate pathogen contamination prior to consumer use, outbreak patterns indicate that more than half involved melons that were cut and not consumed quickly, a result of pathogens on the rind that grow on the sugar-rich interior fruit. This limited study was conducted to assess sources and extent of melon rind contamination in production fields and at processing and packing facilities in the Rio Grande River Valley. Points where melons can become contaminated were identified. In spring 1999, cantaloupe sampled from two sites showed that processed melons often had more bacterial contamination than melons fresh from the field. For instance, washed cantaloupe had more total coliforms than fresh picked cantaloupe. In fall 1999, washing increased total coliforms on honeydew melons and failed to reduce fecal coliforms or enterococci below the 350 per gram of rind present on fresh picked fruit. Hydro-cooler and primary dunk/wash tank water that was poorly chlorinated, not only inadequately removed bacteria, but added them. Sources of coliforms and enterococci included: melon production soils, irrigation water, standing water in the field, and processing facility wash water pumped from the Rio Grande River. Producers/packers may want to consider installation of automatic chlorinators on primary wash tanks, and water quality testing during packing to reduce contamination. Control of wildlife contamination (birds, rodents, etc.) on fresh and processed produce and shipping boxes also need to be addressed.

Technical Abstract:
Multi-state and international foodborne illness outbreaks, particularly involving cantaloupe and often involving rare Salmonella species, have increased dramatically over the past 13 years. This study was conducted to assess the sources and extent of melon rind contamination in production fields and at processing and packing facilities. Points where melons can become contaminated were identified. In spring 1999, cantaloupe sampled from two sites in the Rio Grande River Valley showed that post-harvest processed melons often had more bacterial contamination than melons fresh from the field. For instance cantaloupe in the field had 2.5-3.5 log cfu g-1 total coliforms while washed melons had 4.0-5.0 log cfu g-1. In fall 1999, processing increased total coliforms on honeydew melons from 2.6 log cfu g-1 to 3.7 log cfu g-1 and total and fecal coliforms and enterococci never fell below 2.5 log cfu g-1. A hydro-cooler at another site contaminated cantaloupe rind with up to 3.4 log cfu total and fecal enterococci g-1; only some of these organisms were removed by a secondary rinse with chlorinated water. Sources of coliforms and enterococci were found at high levels in melon production soils especially in furrows that were flood irrigated, in standing water at one field and in irrigation water at both sites. At one processing facility, wash water pumped from the Rio Grande River may not have been sufficiently disinfected prior to use. Since soil, irrigation and process water were potential sources of bacterial contamination, monitoring and management on-farm and at processing and packing facilities should focus on water quality as an important control point for growers and packers to reduce bacterial contamination on melon rinds.